A micro electro-mechanical system (hereinafter, referred to as a MEMS) technology is a technology for combining micro-mechanical devices such as sensors, valves, gears, reflecting minors, and drivers integrated into a semiconductor chip to a computer.
Recently, the MEMS is used for a navigation system, a sensor built in a wing structure of an airplane to sense airflow according to a change of resistance on a surface of the wing of the airplane, an optical switching apparatus for switching optical signals among separate paths at a rate of 20 ns, a sensor-driven air-conditioning system, a sensor built in a base of a building to smoothly change a property of a material according to sensed pressure of the air, and the like. As the most respective MEMS, there is a vibration sensor or a magnetic sensor built in an airbag of a vehicle.
FIG. 1 is a view illustrating an example of a vibration sensor using the MEMS.
Referring to FIG. 1, the vibration sensor 10 includes a moving object M of which position is changed according to a vibration and position of the vibration sensor and two fixed electrodes Es1 and Es2 which are disposed at both sides of the moving object M to obtain electrostatic capacitances Cs1 and Cs1 corresponding to distances from the moving object M.
As the position of the vibration sensor 10 is changed according to an external environment, the position of the moving object M is also changed, so that a distance between the two fixed electrode Es1 and Es2 is also changed. As a result, the electrostatic capacitances Cs1 and Cs1 obtained by the two fixed electrode Es1 and Es2 is changed.
For example, as shown in (a) of FIG. 2, if the vibration sensor 10 is maintained parallel to a reference plane, the distances of the moving object M from the two fixed electrode Es1 and Es2 are equal to each other (d1=d2). Therefore, the electrostatic capacitances Cs1 and Cs1 obtained by the fixed electrode Es1 and Es2 are equal to each other.
However, as shown in (b) of FIG. 2, if the vibration sensor 10 is inclined leftwards with an angle θ, the moving object M is inclined rightwards. Therefore, the distance d2 between the moving object M and the second fixed electrodes Es2 is smaller than the distance d1 between the moving object M and the first fixed electrodes Es1. Accordingly, the electrostatic capacitance Cs2 obtained by the second fixed electrodes Es2 is larger than the electrostatic capacitance Cs1 obtained by the first fixed electrodes Es1.
On the other hand, as shown in (c) of FIG. 2, if the vibration sensor 10 is inclined rightwards with an angle θ, the moving object M is also inclined leftwards. Therefore, the distance d1 between the moving object M and the first fixed electrodes Es1 is smaller than the distance d2 between the moving object M and the second fixed electrodes Es2. Accordingly, the electrostatic capacitance Cs1 obtained by the first fixed electrodes Es1 is larger than the electrostatic capacitance Cs2 obtained by the second fixed electrodes Es2.
In this manner, the vibration sensor 10 of FIG. 1 can change the two electrostatic capacitances Cs1 and Cs2 according to the position thereof, so that the vibration sensor can notify the position thereof.